Delta Air Lines will begin diversity training for all of its flight crews after at least two widely publicized incidents in which passengers said they were discriminated against or treated uncivilly on its flights.

Chief Executive Officer Ed Bastian banned a passenger for life in November after the man was videotaped yelling in support of Donald Trump. A few weeks earlier, the carrier had apologized to a black doctor who volunteered to help a sick passenger and was rebuffed by a flight attendant.

“Their brand reputation is critical, and you don’t want that reputation to be damaged,” said Jason Wingard, dean of Columbia University’s School of Professional Studies and a consultant on diversity issues. Success for consumer-facing companies such as airlines is “tied to customer loyalty and emotions.”

The Atlanta-based airline is last among the four largest U.S. carriers to require such training, which it made mandatory for executives last year and will start for 23,000 flight attendants in the second quarter. Delta’s classes will use “real and relevant scenarios” and discuss unconscious bias and so-called microaggressions, said Keyra Lynn Johnson, managing director for diversity and inclusion. “This goes well beyond the typical cross-cultural training.”

Tensions between passengers or between passengers and crew have been on the rise. On Friday, the U.S. Department of Transportation issued new guidelines for airline personnel on nondiscrimination, including sample scenarios outlining their legal obligation not to discriminate based on race, sex, religion or national origin. It also issued a document for passengers, explaining their rights.

Incidents of reported discrimination rose 37 percent in the first 10 months of 2016 to 74, according to the transportation agency. Though the number is fairly small, these episodes can cause public relations headaches for the companies and provoke lawsuits.

The U.S. presidential campaign, in which Trump proposed banning Muslims from the U.S., and recent terrorist incidents have intensified the issue, said Corey Saylor, director of the department to monitor and combat Islamophobia at the Council for American-Islamic Relations. The organization documented 149 removals from flights, buses or trains in the first nine months of last year, more than double the 62 of the same period a year earlier, he said.

The four Transportation Department scenarios included a headscarf-wearing woman, two men speaking Arabic and a Sikh. The department advised flight crew to react to passengers based on their behavior, rather than their appearance.

Delta moved up its training plan after an October flight in which a passenger was taken ill. After a call went out for a doctor, physician Tamika Cross came forward. She was brushed off by a flight attendant who said “Oh no sweetie, we are looking for actual physicians,” Cross said in a Facebook account of the episode that has been shared 48,000 times.

Cross, who is African American, complained to the airline’s top management, which has also decided to no longer require physicians to show credentials on flights.

“We’re using this incident and others as an opportunity to improve,” said Brian Kruse, a Delta spokesman.

The Trump supporter’s outburst prompted Bastian to ban the passenger for life and refund others’ tickets. “The heightened tension in our society means that now more than ever, we must require civility on our planes,” Bastian said in a memo to employees.

American Airlines Group, the world’s largest carrier, has a “value of respect” training that’s required for all flight attendants with a refresher every two years. Southwest Airlines gives mandatory anti-discrimination and anti-harassment courses to new hires, and optional diversity training thereafter.

At United Airlines, all customer-facing employees, including its 25,000 flight attendants, undergo recurrent diversity training that includes lessons in cultural awareness.

“What we have seen is a higher sense of emotion across the board, and that’s something that flight attendants have been aware of, and put on their checklist,” said Sara Nelson, president of the Association of Flight Attendants-CWA, which represents crews at several airlines including United. Most carriers first began such training after 9/11, Nelson said. American and Southwest also have unionized flight attendants, while Delta does not.

While more companies are adopting diversity training, “it’s usually reactive,” said Columbia’s Wingard. “They may do leadership training, but diversity training, in particular, is usually absent until something happens -- a lawsuit, or a public relations disaster,” he said.

The airline industry’s woes hold a lesson for other companies in consumer-facing businesses, from travel to sales, he said. “Even if they do have diversity training, it’s much more aligned with the office employees,” he said.

Requiring training of everyone who deals with customers would mean that “all of a sudden diversity training would take on a new meaning,” Wingard said.